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BACKGROUND: Between 1992 and 2011, 373 Canadian individuals with adverse anesthetic reaction were referred to the Malignant Hyperthermia Unit in Toronto, Ontario, Canada for malignant hyperthermia (MH) diagnostic testing. We analyzed the epidemiologic characteristics of the index adverse anesthetics for those probands who were confirmed to be MH susceptible.

METHODS: One hundred twenty-nine proband survivors of adverse anesthetic reactions, whose MH susceptible status was confirmed by caffeine-halothane contracture testing were selected. Individuals were excluded if the index anesthetic record was not available for review. Data regarding demographics, clinical signs, laboratory findings, treatment, and complications were retrospectively compiled and analyzed. A Fisher exact test and χ2 test were applied to compare categorical variables. The Wilcoxon rank-sum test was applied with continuous variables.

RESULTS: Young males (61.2%) dominated among selected patients. Seventeen of 129 (13.2%) patients had prior unremarkable anesthesia. Anesthetic triggers were volatile-only (n = 58), succinylcholine-only (n = 20), or both volatile and succinylcholine (n = 51). Eight (6.2%) cases occurred in the postanesthetic care unit. There were no reactions after discharge from the postanesthetic care unit. The most frequent clinical signs were hyperthermia (66.7%), sinus tachycardia (62.0%), and hypercarbia (51.9%). Complications occurred in 20.1% of patients, the most common complication being renal dysfunction. When 20 or more minutes between the first adverse sign and dantrolene treatment elapsed, complication rates increased to ≥30%.

CONCLUSIONS: This is the first Canadian study in 3 decades to report nationwide data on MH epidemiology. Features that differ from earlier reports include a 15.5% incidence of reactions triggered by succinylcholine alone and lower complication rates. In agreement with previously published studies, we confirmed in this independent dataset that increased complication rates were associated with an increased time interval between the first adverse clinical sign and dantrolene treatment. This underscores the need for early diagnosis and rapid dantrolene access and administration in anesthetizing locations using either succinylcholine or volatile anesthetic drugs.

Published ahead of print July 10, 2013

From the *Malignant Hyperthermia Investigation Unit, Toronto General Hospital, University Health Network; †Department of Anesthesia, University of Toronto, Toronto, Ontario, Canada; ‡The North American Malignant Hyperthermia Registry of the Malignant Hyperthermia Association of the United States, Pittsburgh, Pennsylvania; and §Toronto, Ontario, Canada.

Accepted for publication March 11, 2013.

Published ahead of print July 10, 2013

Funding: This work was funded by the Department of Anesthesia, University of Toronto Merit award to Sheila Riazi. Duminda Wijeysundera is supported by a Clinician-Scientist award from the Canadian Institutes of Health Research (Ottawa, Ontario, Canada) and a Merit award from the Department of Anesthesia at the University of Toronto (Toronto, Ontario, Canada).

The paper was presented at the annual meeting of the European Malignant Hyperthermia Group (EMHG), Basel, Switzerland, May 2013.